We present a systematic study of angular-dependent magnetization reversal in approximately 20-µm-thick epitaxial $\left({\mathrm{Bi}}_x{\mathrm{La}}_y{\mathrm{Y}}_{3-x-y}\right)\left({\mathrm{Fe}}_{5-z}{\mathrm{Ga}}_z\right){\mathrm{O}}_{12}$ garnet films having different Bi concentrations. All films exhibit robust perpendicular magnetic anisotropy and maintain very low Gilbert damping of the order of ${10}^{-4}$. By analyzing hysteresis behavior for different magnetic field orientations β, the nature of irreversible magnetization processes is studied over a wide angular range. Our results show that nucleation-dominated hysteretic reversal emerges only within a finite angular range near the out-of-plane orientation (approximately $\beta ={60}^{\circ }\text{–}{120}^{\circ }$ from in-plane orientation), whereas outside this range magnetization reversal is initiated via nonhysteretic instability. We also find that the angular range, in which nucleation processes occur, increases synchronously with the perpendicular anisotropy of our samples upon increasing their Bi concentration. The quantitative evolution of the observed nucleation field versus magnetic field angle β deviates markedly from a simple geometric projection onto the surface normal, which would be proportional to 1/sinβ. Nonetheless, we observe that the nucleation field increases as the field deviated from aligning with the surface normal for all our samples in contrast to prior observation in other material systems. Our findings demonstrate that despite the relevant perpendicular anisotropy of our samples, domain nucleation processes in thick garnet films are not governed solely by the perpendicular field components. Instead, our quantitative analysis illustrates that in-plane field components must be considered as an essential correction. These findings establish a coherent physical picture of magnetization reversal in thick garnet films for arbitrary magnetic field orientation.

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• Demagnetization
• Magnetic anisotropy
• Magnetic domains
• Magnetic phase transitions
• Magnetic texture
• Magnetization switching
• Magnetic thin films
• Magnetic techniques
• Magnetization measurements